Hypothermia is routinely used during cardiac surgical procedures. In addition, accidental hypothermia is encountered in trauma, exposure, and during operations with open body cavities. Hypothermia alters every hemodynamic, metabolic, and gas transfer parameter. Our laboratory and clinical research is aimed at lessening the deleterious effects of hypothermia and of enhancing the beneficial changes produced by hypothermia. The present study was designed to evaluate the effects of two different pH management schemes (alpha-stat and pH-stat) on systemic hemodynamics, myocardial function, and systemic metabolism in the dog during hypothermia. Previous investigators have suggested that the alpha- stat scheme might lead to increased metabolism during hypothermia, thus negating the beneficial decrease in oxygen consumption produced by hypothermia. Dogs were surface-cooled to 26oC and hemodynamic and metabolic parameters measured. The results were that the only difference between alpha-stat and pH-stat animals was that the mean arterial pressure during hypothermia was lower in the alpha-stat animals. Systemic oxygen consumption was no different between the groups and the Q10 was not different. The base excess eas increased in the alpha-stat group. There was no lactate production in either group. These results show that there are few hemodynamic or metabolic differences between moderate hypothermia in surface-cooled dogs during alpha-stat or pH-stat blood pH management. In particular, the pH-stat strategy does not produce a greater decrease in metabolism than the alpha-stat pH strategy during hypothermia. Oxygen delivery to the tissues is adequate with either pH strategy. Experimental and clinical evidence from this laboratory supports the use of alpha-stat pH management during hypothermia.